In conjunction with P. Qasba, A. Dandekar and S. Safaya: Expression of milk protein and other genes in different hormone environments has been examined in normal and neoplastic rat mammary tissues. We studied the effects of ovariectomy during pregnancy, perphenazine administration, and a mammotropic hormone secreting pituitary tumor. The general pattern of gene expression was monitored by translating total poly A(+)RNAs in a wheat germ protein synthesis extract and subjecting the translation products to one- and two-dimensional polyacrylamide gel electrophoresis. Specific poly A(+)RNAs were monitored by filter hybridization to probes made from cDNA clones for abundant lactating mammary gland poly A(+)RNAs. Expression of alpha-lactalbumin was examined in detail using immunological methods and by gel electrophoresis.